Evidence of a Kondo Destroying Quantum Critical Point in YbRh₂Si₂

Abstract

The heavy-fermion metal YbRh$_{2}$Si$_{2}$ is a weak antiferromagnet below\n$T_{N} = 0.07$ K. Application of a low magnetic field $B_{c} = 0.06$ T ($\\perp\nc$) is sufficient to continuously suppress the antiferromagnetic (AF) order.\nBelow $T \\approx 10$ K, the Sommerfeld coefficient of the electronic specific\nheat $\\gamma(T)$ exhibits a logarithmic divergence. At $T < 0.3$ K, $\\gamma(T)\n\\sim T^{-\\epsilon}$ ($\\epsilon: 0.3 - 0.4$), while the electrical resistivity\n$\\rho(T) = \\rho_{0} + aT$ ($\\rho_{0}$: residual resistivity). Upon\nextrapolating finite-$T$ data of transport and thermodynamic quantities to $T =\n0$, one observes (i) a vanishing of the "Fermi surface crossover" scale\n$T^{*}(B)$, (ii) an abrupt jump of the initial Hall coefficient $R_{H}(B)$ and\n(iii) a violation of the Wiedemann Franz law at $B = B_{c}$, the field-induced\nquantum critical point (QCP). These observations are interpreted as evidence of\na critical destruction of the heavy quasiparticles, i.e., propagating Kondo\nsinglets, at the QCP of this material.\n